This invention relates to the synthesis of crystalline aluminum phosphates with a urea templating agent.
Aluminum phosphates are taught in U.S. Pat. Nos. 4,310,440 and 4,385,994, for example. Aluminum phosphate materials have electroneutral lattices and, therefore, are not useful as ion-exchangers or as catalyst components. Microporous aluminum phosphates may have water and/or organic amine or quaternary ammonium salt entrapped within the aluminum phosphate. The amine or ammonium salt may play a role as crystallization template. Because of the aluminum/phosphorus atomic ratio of these materials is about unity, they display virtually no ion-exchange properties, the framework positive charge on phosphorus being balanced by corresponding negative charge on aluminum: EQU AlPO.sub.4 =(AlO.sub.2.sup.-)(PO.sub.2.sup.+).
The pores of these microporous aluminum phosphates may be uniform and have nominal diameters within the range of about 3 to 10 Angstroms, an intracrystalline adsorption capacity for water at 4.6 torr and 24.degree. C. of at least 3.5 weight percent, the adsorption and desorption of water being completely reversible while retaining the same essential framework topology in both the hydrated and dehydrated state.